Every deduction you might want to fill can be filled in as you wish in the process as the form allows that. Every possibly relevant value known to the system is simply pre-filled, and otherwise manually entered data is imported year over year. For example I deduce the real costs of my commute instead of the default 10% deduction, and both the value and comments (which include the detailed calculations, because I'm nice to the other side) are there. I only have to make a few minor adjustments, and voila.